A. 6
B. 8
C. 12
D. 12.5
E. 12.8
Answer: E
Explanation:
Speed of “moving walkway” = 96 inches per second
Converting to feet per second
Speed of “moving walkway” = 8 feet per second
Speed at which Miami moves = 72 inches per second = 6 feet per second
Combined speed = 14 feet per second
Miami covers 180 feet at a relative speed (with a group of people moving in the same direction) of 14 – 8 = 6 feet/sec.
Time taken to cover 180 feet = 180/6 = 30 sec
Distance covered in 30 secs = 14*30 = 420 feet
Now the remaining distance to cover is 480 – 420 = 60 feet
60 feet is covered with only the speed of moving walkway.
i.e.,
Time taken to cover 60 feet = 60/8 = 7.5 feet per second
Average Speed = \frac{Total Distance}{Total Time Taken} =\frac{480}{30 + 7.5} =\frac{480}{37.5}=\frac{192}{15}=\frac{64}{5}=12.8
Hence the answer is E.

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